Effect Of Finite Thickness Research Articles

Effect of substrate thickness and metallization thickness on dispersion characteristics of CPW

Approximate conformal mapping techniques have been used for analysing the effect of finite substrate thickness on coplanar wave guide (CPW). Calculations for impedance and effective dielectric constant are presented for CPW's with finite substrate thicknesses. Analytical formulation are presented for calculations. Network analytical methods of electromagnetic fields are employed to evaluate the effect of thick metal coating on CPW. Dispersion characteristics of CPW have been plotted for various metallization thicknesses. Effect of thick metal coating on guide wavelength is also plotted. Increase in metallization thickness of CPW causes an increase in wavelength. Due to this fact characteristic impedance and effective dielectric constant decreases.

Quantitative analysis of trabecular microstructure by 400 MHz nuclear magnetic resonance imaging

A new approach for the quantitative analysis of trabecular microstructure, based on high-field proton nuclear magnetic resonance (NMR) imaging, is presented. NMR is ideal because it provides high contrast between the marrow proton signal and the bone, which appears with background intensity. Images from 1 cm3 defatted specimens of trabecular bone, suspended in water doped with 1 mM Gd(DTPA) to shorten T1 to about 300 ms, can be obtained at a resolution on the order of 30-50 microns and slice thickness of 150 microns, in 10 minutes at 400 MHz proton frequency. Digital image processing algorithms were designed and evaluated for the measurement of bone area fraction, perimeter length, mean trabecular thickness, and separation. Bone area fraction derived from the NMR images was found to be in excellent agreement with bone volume fraction measured independently (slope = 0.96, r2 = 0.924, p < 0.0001). Errors in the mean trabecular thickness and separation were < 6%. The effects of finite imaging slice thickness and signal-to-noise ratio (SNR) were also evaluated. The data suggest a resolution of 50 x 50 x 200 microns 3 and an SNR on the order of 10 to provide safe margins for precise and accurate structural analysis by means of the algorithms presented in this paper. The method allows simultaneous measurement at multiple locations within the specimen volume without the need for physical sectioning.

Exchange energy for electrons in two dimensions: Effects of finite temperature and finite thickness.

Exchange energy for electrons in two dimensions: Effects of finite temperature and finite thickness.

Mixed amphiphilic bilayers: Bending elasticity and formation of vesicles

In this article, we report on a theoretical investigation of the bending elasticity of fluid bilayers consisting of two amphiphilic species. According to the ideas of Safran et al. [Phys. Rev. A 43, 1071 (1991)], one expects that the corresponding composition degree of freedom couples to curvature playing so a significant role in the bending properties of the mixed membrane. We show that these properties can be interpreted in terms of the bending moduli of the individual constituting monolayers provided that these are calculated at fixed chemical potential μ and not at fixed composition. A simple general theory is built up, designed so that the μ moduli can be calculated in a consistent way. It is shown that the composition degree of freedom softens the mean curvature modulus κ but leaves the Gaussian modulus κ̄ unaffected. Finite thickness effects are also considered. They do not modify κ, whereas their influence on κ̄ just has the same value as formerly calculated for the case of no composition degree of freedom. Finally, this general approach is applied to more specific models of mixed membranes: (i) bilayers made of surfactant and cosurfactant; (ii) initially neutral membranes weakly charged by addition of a small amount of an ionic surfactant; and (iii) bilayers covered with a brush of adsorbed end-functionalized polymers. New insights are also obtained on well known experimental facts such as the existence of spherulite textures in lamellar phases and spontaneous formation of vesicles and liposomes.

Thermoacoustic heat transportation and energy transformation Part 1: Formulation of the problem

This paper discusses the acoustic wave motion, time-averaged thermoacoustic heat transportation and energy transformation in sound channels. The thermoacoustic effects are caused by the thermal interaction of the oscillatory gaseous fluid and the solid wall media. A closed set of longitudinal thermoacoustic equations: the wave equation, governing the acoustic wave motion, and the energy-temperature equation, governing the energy flux and temperature distribution, were obtained. The effects of finite solid wall thickness, finite heat exchange between the solid outer wall and its environment, and factors relating to the viscid and real gas fluid are taken into consideration. This set of thermoacoustic equations, together with other thermoacoustic relations, form a closed and complete mathematic modelling of acoustic wave motion, thermoacoustic heat transportation and energy transformation.

Surface impedance of YBa2Cu3O7−x thin film grain boundary Josephson junctions: Evaluation of the I cR n product

The temperature and the dc magnetic field dependence of the effective surface impedance Zs of epitaxial YBa2Cu3O7−x thin films on [001] tilt SrTiO3 bicrystals with tilt angles of 36.8° and 24° have been investigated at 87 GHz. The effects of the grain boundaries become increasingly important with decreasing characteristic voltage IcRn and increasing unit areal normal resistance RnA. The boundaries can consistently be described with a resistively shunted Josephson transmission line model taking into account the effect of finite film thickness. Thermal or magnetic loading of the junction leads to additional losses, whereas the effective microwave penetration depth exhibits a specific extremal behavior. From the magnetic response of Zs at 4.2 K, the junction lower critical fields as well as the values of IcRn and RnA can be deduced. The data agree well with dc transport measurements.

Strain-induced helimagnetism, finite thickness effects, and interlayer coupling in magnetic semiconductor multilayers

Neutron diffraction studies of antiferromagnetic semiconductor superlattices are reviewed. Mn-VI/II-VI multilayers (e.g. MnSe/ZnTe, MnSe/ZnSe) exhibit a variety of strain-induced effects in spin ordering and phase transition phenomena. In MnTe/CdTe systems, in which the thickness of the non-magnetic CdTe spacers can be very thin (∼ 6 Å) and comparable with the range of the Mn-Mn exchange interactions, the measurements clearly show the onset of interlayer coupling. Pronounced interlayer coupling has been observed in experiments on another system, EuTe/PbTe, with much thicker (30–40 Å) non-magnetic layers - arguably, this coupling is maintained by dipolar fields.

Field-effect conductance in amorphous silicon thin-film transistors with a defect pool density of states

A new computer program to analyze field-effect conductance measurements has been developed. In this program a defect pool model, where the equilibrium density of state is determined by the Fermi level, has been incorporated. Transistors with finite band bending, due to fixed charge in the insulator, will therefore have a density of states that is spatially inhomogeneous. The inhomogeneous density of states means that the subthreshold slope of a device is not always controlled by the density of states near the interface, but can become dominated by the bulk density of states, contrary to simpler models. Both electron and hole branches are modeled simultaneously and self-consistently with no assumptions made about the flatband voltage. Indeed, it is demonstrated that there is no flatband voltage in a transistor with an inhomogeneous density of state; however, a true flatband voltage can be achieved by a process of thermal bias annealing. Finite thickness effects and defect correlation energies are taken into account. The program is used to model the characteristics of thin-film transistors both before and after thermal bias annealing. The model fits the experimental results well, even though there are few free parameters. A key result is that the defect pool parameter Δ is determined, which is the energy separation of the D0/− transition observed in n-type material and the D+/0 transition in p-type material. It is found that Δ=0.44 eV for all devices fitted, which suggests this a fundamental parameter of a-Si:H. This value of Δ implies that there are about four times as many charged as neutral devices in bulk intrinsic amorphous silicon.

Direct submillimeter absorptivity measurements on epitaxial Ba 1−xK xBiO 3 films at 2K

We have used a bolometric technique to obtain accurate low temperature loss data for epitaxial thin films of Ba 0.6K 0.4BiO 3 from 30 cm −1 to 700 cm −1. These films were grown on MgO and SrTiO 3 substrates by MBE, off-axis sputtering and laser deposition techniques. All films show a strong absorption onset near the BCS tunneling gap of 3.5k BT c. We have analyzed these data using a Kramers-Kronig transformation and have corrected for finite film thickness effects. Our results indicate that the absorption onset is consistent with a superconducting energy gap. Comparison is made with predictions based on strong coupling Eliashberg theory using α 2F(ω) spectra obtained from the literature. While we are able to fit the overall measured absorptivity, we are unable to fit the structure observed in our data.

The effect of finite film thickness on the surface segregation in symmetric binary polymer mixtures

We report neutron reflectivity and dynamic secondary ion mass spectroscopy measurements of surface segregation from symmetric, isotopic polystyrene blends, spin coated onto oxide covered silicon wafers, as a function of film thickness. The results of this analysis show that the segments of the deuterated polymer always partition to both the air and the substrate interfaces. Furthermore, the surface segregation is affected significantly if the film thicknesses are reduced below ∼four times the correlation length in the systems, and the segregation to both surfaces decreases with decreasing thickness. These results are in good agreement with the predictions of a mean-field lattice model which incorporates composition and chain length independent values of the surface energy parameter χs at each surface.

Measurement of the microwave dielectric constant for low-loss samples with finite thickness using open-ended coaxial-line probes

This work addresses the effect of finite sample thickness on microwave dielectric constant measurements for thin, planar, low-loss samples using the open-ended coaxial-line probe method. Detailed measurements of the dielectric constant were carried out on a wide range of thicknesses of air samples which were backed by infinitely thick teflon and alumina dielectric media. The measurements were made at room temperature for various (50 Ω) coaxial-line dimensions, microwave frequencies 4–8 GHz, and power levels near a fraction of a mW. The results provide strong support for previously published theoretical calculations based on a boundary value problem which uses a spectral domain formulation for the aperture fields. From thin, planar samples, values of 10.4±0.5 and 25.9±1.3 were obtained at 5 GHz and 300 K for the bulk dielectric constant of MgO and LaAl2O3, respectively. The applicability of a simple empirical model based on an exponential fit is discussed.

Modeling of nonlinear absorption and refraction in quantum-well structures for all optical switching

A realistic model of the electromagnetic response in excited, type-I semiconductor quantum wells is presented. A multisubband analysis of the room temperature band edge spectra, in which the plasma effects are determined through an iterative, numerical solution of a generalized Bethe-Salpeter equation, is introduced. The method allows the treatment of situations in which transitions higher than the first give sizeable contributions to the nonlinear optical properties, as in coupled quantum wells or in the propagation of TM modes within waveguides based on quantum confined structures. Further, the method accounts for the effects of finite quantum-well thickness and incorporates a phenomenological description of the width of the resonance lines. The behavior is compared to that exhibited by more idealized models introduced in earlier works, where single-subband, purely 2-D systems were treated. Computer generated spectra are compared with absorption spectra experimentally obtained for moderately strained InGaAs-InP QWs. >

The influence of metallization thickness on the characteristics of cascaded junction discontinuities of shielded coplanar type transmission line

A full-wave analysis based on the mode-matching technique is applied to analyze cascaded junction discontinuities of coplanar-type transmission lines, coplanar waveguide (CPW) and finline. Results for a CPW-finline transition, a shielded CPW gap and a symmetric notch incorporating the finite metallization thickness effect are presented. The influence of metallization thickness on the coupling effect exhibited by cascaded junction discontinuities is also presented and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The influence of finite conductor thickness and conductivity on fundamental and higher-order modes in miniature hybrid MIC's (MHMIC's) and MMIC's

The effect of finite metallization thickness and finite conductivity on the propagation characteristics of conductor-backed CPW on thin substrate is rigorously analyzed. A self-consistent approach is used together with the method of lines (MoL) to determine the propagation constant, losses and field distribution of the fundamental and first two higher-order modes in coplanar waveguides (CPWs) with finite metallization thickness and lossy backmetallization. The method used is general and can be applied to miniature MHMICs and MMICs including lossy semiconductor substrate. It is shown that the onset of higher-order modes limits the usable frequency range of conductor-backed CPWs. The analysis also includes microstrip transmission lines on thin substrate material. It is demonstrated that a resistive strip embedded into the microstrip ground plane may potentially be useful in the design of integrated planar attenuators. >

Automated image analysis of ice thin sections — instrumentation, methods and extraction of stereological and textural parameters

AbstractImage-analysis procedures have been developed for a simple PC-based system to evaluate the textural features of ice thin sections automatically. The method yields parameters that describe both ice crystals and pores in an objective, reproducible manner. Specimens are recorded in linearly and circularly polarized light (ice grains) as well as in transmitted and incident plain light (pores) under standardized conditions. After preparative filtering, images are segmented through union of two Sobel-filtered images (ice crystals/grain boundaries) or through thresholding (ice crystals/pores). The quantification of texture is based on the evaluation of image contrast as well as on linear analysis and non-linear transforms to obtain information on grain-sizes and their distribution. In the study of ice pores, stereological effects of finite section thickness have to be corrected. The discussion focuses on errors involved in automated textural analysis and the glaciological yield of measured and derived parameters.

Automated image analysis of ice thin sections — instrumentation, methods and extraction of stereological and textural parameters

AbstractImage-analysis procedures have been developed for a simple PC-based system to evaluate the textural features of ice thin sections automatically. The method yields parameters that describe both ice crystals and pores in an objective, reproducible manner. Specimens are recorded in linearly and circularly polarized light (ice grains) as well as in transmitted and incident plain light (pores) under standardized conditions. After preparative filtering, images are segmented through union of two Sobel-filtered images (ice crystals/grain boundaries) or through thresholding (ice crystals/pores). The quantification of texture is based on the evaluation of image contrast as well as on linear analysis and non-linear transforms to obtain information on grain-sizes and their distribution. In the study of ice pores, stereological effects of finite section thickness have to be corrected. The discussion focuses on errors involved in automated textural analysis and the glaciological yield of measured and derived parameters.

Analysis of a strip loaded resonant longitudinal slot in the broad wall of a rectangular waveguide

A longitudinal slot at the centre of the broad wall of a rectangular waveguide in the presence of one or two vertical strips has been analysed. The combination is excited by the dominant TE01 mode, and the slot radiates externally. The effect of finite thickness of the waveguide walls has been taken care of by treating the slot as a stub waveguide. The coupled integral equations are solved using Galerkin&apos;s technique. The resultant coefficients are used to compute the dominant mode scattering parameters and hence the equivalent T-network. The possibility of obtaining a resonant condition for the radiating centred slot–strip combination has been established. Design data derived in this study eliminate the need to gather initial input data experimentally.

Finite grid radius and thickness effects on retarding potential analyzer measured suprathermal electron density and temperature

The effect of finite grid radius and thickness on the electron current measured by planar retarding potential analyzers (RPAs) is analyzed numerically. Depending on the plasma environment, the current is significantly reduced below that which is calculated using a theoretical equation derived for an idealized RPA having grids with infinite radius and vanishingly small thickness. A correction factor to the idealized theoretical equation is derived for the Pioneer Venus (PV) orbiter RPA (ORPA) for electron gasses consisting of one or more components obeying Maxwell statistics. The error in density and temperature of Maxwellian electron distributions previously derived from ORPA data using the theoretical expression for the idealized ORPA is evaluated by comparing the densities and temperatures derived from a sample of PV ORPA data using the theoretical expression with and without the correction factor.

Stability of thick two-component galactic discs

The thickness scales and the local parameters relevant to both the equilibrium and stability of two-component galactic disks are studied. The results obtained, as regards the vertical structure at equilibrium of two-component galactic disks, are used to investigate their local linear stability properties. Under reasonable assumptions, finite-thickness corrections to the local dispersion relation can be expressed in terms of two reduction factors weakening the response of the two components or, equivalently, lowering their equilibrium surface densities. An ansatz for such reduction factors, justified by extending the analysis performed for one-component purely stellar disks, is made, and the corresponding two-fluid marginal stability curve is studied in standard star-dominated and peculiar gas-dominated regimes. It is found that the stabilizing role of finite-thickness effects can partially counterbalance the destabilizing role of the cold interstellar gas in linear regimes.

Computing boundary forces due to unsteady, inviscid, incompressible flow

Recently, several investigators have implemented time-accurate finite difference simulations of incompressible flows based on the method of artificial compressibility. Here we validate the method against the discrete vortex method on the problem of a compact vortex being convected by an inviscid mean flow through a converging/ diverging channel. This can be regarded as a model problem that isolates the effect of finite airfoil thickness on the interaction of a cascade with a nonuniform inflow. Good qualitative agreement between the computed pressure and vorticity fields is shown. A quantitative comparison is made of the unsteady force on the channel walls. We demonstrate the numerical use of a volume-integral formula for computing the unsteady force. In the case of the finite difference method, more accurate results were obtained from this formula than by simply integrating the surface pressure on the channel walls due to the reduced accuracy of the solution near the boundaries. We also describe a direct way of computing pressure with the discrete vortex method.